1. Field of the Invention
The present invention relates generally to an imaging apparatus that includes two imaging optical systems that change image focusing locations, respectively, and two imagers that convert subject images formed by the two imaging optical systems into image signals, respectively.
2. Description of the Related Art
Methods of Automatic Focusing (AF) in a digital camera including imagers, such as a Charge Coupled Device (CCD) and a Complementary metal-oxide-semiconductor (CMOS), include a method called contrast AF, which scans and moves an image focusing location of an imaging optical system, acquires a contrast evaluation value in each image focusing location, detects an image focusing location having a contrast evaluation value, which is an extremum, and determines the detected image focusing location as a focus location.
FIGS. 12A to 12E illustrate an operation of a conventional imaging optical system for detecting a focus location by contrast AF.
Referring to FIGS. 12A to 12E, in the graphs, the dotted curve corresponds to a contrast evaluation value that is not yet determined yet, and the solid line corresponds to a part having already acquired a determined contrast evaluation value. When the image focusing location stays at an initial focus location, as illustrated in FIG. 12A, it is not clear which side, between the infinity (INF) side and the NEAR side, the renewed focus location is nearer to from the current image focusing location. Accordingly, the image focusing location is first scanned and moved in some degree in toward the INF or NEAR side to determine whether the contrast evaluation value increases or decreases. Thereafter, it is estimated that the focus location is nearer to the side corresponding to the increasing direction, before starting the operation.
In this operation, because it is initially unclear which side the renewed focus location is nearer to from the current image focusing location, i.e., either the INF side or the NEAR side, the current image focusing location may be moved toward a side opposite to the extremum as illustrated in FIG. 12B.
Then, as illustrated in FIG. 12C, it is required to unnecessarily perform an extra movement of the image focusing location by the distance required in order to return the image focusing location to the original position.
Thereafter, the image focusing location is continuously changed until the contrast evaluation value changes from the increasing trend to the decreasing trend as illustrated in FIG. 12D, and the renewed focus location is then determined by returning an over-moved image focusing location to the renewed focus location as illustrated in FIG. 12E, thereby completing the contrast AF.
In the contrast AF as described above, in an initial stage, a user cannot know which side the renewed focus location is nearer to from the current image focusing location. Therefore, especially as illustrated in FIG. 12B, the image focusing location may be moved away from the renewed focus location. In this case, the time necessary for the automatic focusing may be prolonged or it may be difficult to perform a smooth operation.
One method for solving the above-described problems is a called “wobbling”. In wobbling, a direction toward the focus location is detected based on the trend of increasing or decreasing a contrast evaluation value acquired by minutely moving the focus lens back and forth, as illustrated in FIG. 13.
In wobbling, there is no possibility to fail in detecting the operation direction when the image focusing location is changed toward a renewed focus location. However, because the focus lens is always driven, this method requires high power consumption, which reduces battery duration.
In a stereoscopic camera having two imaging optical systems for imaging a stereoscopic image, estimation for a direction of a focus location is not especially performed. Instead, the scanning range for contrast AF is distributed to the two focus lenses of the two imaging optical systems, in order to reduce the time for the AF to a shortest time, e.g., up to nearly one-half of the original time.
For example, a double lens camera as described in Japanese Patent Unexamined Publication No. 2006-162990 includes a first imaging optical system and a second imaging optical system, and may separately control locations of respective lenses 13. Further, if the user partially pushes a shutter button, e.g., to a degree of one-half, to start an AF operation, a focus lens 13 of the first imaging optical system is moved toward the INF end, a focus lens 13 of the second imaging optical system is moved toward the NEAR end, and respective focus lenses 13 are scan-moved to a center side as illustrated in FIG. 14, in order to find an image focusing location having a peak contrast evaluation value.
Further, in another example described in Japanese Patent Unexamined Publication No. 2006-162990, as illustrated in FIG. 15, if the user partially pushes a shutter button, e.g., to a degree of one-half, to start an AF operation, the focus lens 13 of the first imaging optical system is substantially arranged at a center of a drivable range, a focus lens 13 of the second imaging optical system is arranged at the NEAR end, and respective focus lenses 13 are then scan-moved to the INF end while maintaining a spacing distance between them, in order to detect a focus location in an imaging optical system.
As noted from the foregoing examples, in a double lens camera, the distribution of the scan-movement range to the two lenses helps reduce the time for the AF, up to nearly one-half of the original time.
However, in the contrast AF method described in Japanese Patent Unexamined Publication No. 2006-162990, in order to distribute the scanning range and to eliminate the necessity for consideration of the driving direction, the focus lens still needs to be moved first to predetermined positions, including the INF side, the NEAR side, and the center, such that a driving time is still incurred for this portion of the operation. That is, because to the conventional methods cannot start the focusing operation at the current image focusing location, the time or power consumption required for an initial arrangement increases.
Further, according to the renewed focus location or the image focusing location before the focusing operation, the initial arrangement operation may require an operation of returning the image focusing location having passed a renewed focus location to the renewed focus location, which may also cause an unnecessary movement, e.g., as illustrated in FIG. 12B.